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3 pin fan - 4 pin fan header

I'm getting a GIGABYTE GA-MA785GM-US2H board for a rebuild I'm doing. I'm also replacing the existing generic case fan and replacing it with a Noctua NF-B9 92mm fan. The problem I'm seeing is that the Noctua has 3 pin connectors only (it does have a 3 pin to Molex adaptor) and the only system fan header is a 4 pin. I know I can connect the fan directly to the PSU but won't I then lose the RPM sensor showing fan speed? Will the 3 pin connector work on the 4 pin header or do I have to get some kind of adaptor to make it work?

Re: 3 pin fan - 4 pin fan header

The yellow wire in both setups is to monitor fan speed.
The fourth wire is for PWM fan speed control.
Look closely at both red boxes and you'll see that the locating tab on the 4-pin mobo header is offset a bit so that you can properly use a 3-pin connector.

Follow Chike's voltage setting recommendation for the 3-pin fan connection and you'll be good to go.

Re: 3 pin fan - 4 pin fan header

Originally Posted by Chike

The 4 pin is compatible with 3 pin fans but if you choose smart fan controll you should select voltage instead PWM.

Thanks for the reply and information. I'm not quite sure what you mean about if you choose smart fan control select voltage instead PWM. Is that applicable for the system fan? The manual for the motherboard shows setting adjustments for the CPU fan but not the system fan. Would I use EasyTune as suggested below?

Re: 3 pin fan - 4 pin fan header

Originally Posted by profJim

The yellow wire in both setups is to monitor fan speed.
The fourth wire is for PWM fan speed control.
Look closely at both red boxes and you'll see that the locating tab on the 4-pin mobo header is offset a bit so that you can properly use a 3-pin connector.

Follow Chike's voltage setting recommendation for the 3-pin fan connection and you'll be good to go.

Thanks for that information. I can now see the tab you mention and how it allows the 3-pin connector to be used.

I've posted a reply to Chike's reply with a question about being able to adjust the System Smart Fan Control as per his suggestion. It's a bit confusing in the MB manual.

Is there any reason for me to be concerned about adding a North Bridge cooler or fan? This build is never going to be used for gaming, video editing, etc., just light applications and Internet.

Re: 3 pin fan - 4 pin fan header

Sorry I should have said select CPU Smart Fan Mode Voltage.
At least with my board if I leave CPU Smart Fan Control on Auto is simply does nothing (disabled).
This option only throttle down fan speed if the CPU is cool enough to reduce noise.

Re: 3 pin fan - 4 pin fan header

Thanks for the clarification Chike. In the manual it says to set to voltage for a 3 pin CPU fan. The stock heatsink fan included with the AMD Athlon II X2 250 Regor 3.0 GHz 2x1 MB L2 Cache Socket AM3 65W Dual-Core CPU that I'm using for this rebuild has a 4-pin connector, same as the header on the MB. The manual indicates that should be set to PWM for a 4-pin fan. Is that correct or should I set to Voltage as you suggest?

Sorry about all the questions but I'd like to get it right. My OP was in regards to the case fan connection and now we're talking about the CPU fan, correct?

CPU Smart FAN Mode
Specifies how to control CPU fan speed. This item is configurable only if CPU Smart FAN Control is set to Enabled.

Re: 3 pin fan - 4 pin fan header

PWM for 4 pin, but you have said you are going to replace it with a Noctua NF-B9 92mm which only has 3 pin so I suggested voltage.
Honestly I have never had the chance to use PWM as I re[laced the Mugen original gan with more powerfull one that only has 3 pins. Most time fan is at 680 RPM and vitualy completely silent.

EDIT: yes we are talking about the CPU fan. Sorry i miss read the OP/ It seems to make no difference which fan you are using for SYS_FAN as the 4th pin is reserved.

Re: 3 pin fan - 4 pin fan header

OK, last question (for now). The Noctua NF-B9 has 2 resistor adaptors included with it. The default wiring is set for 1600 RPM. Using adaptor 1 changes the default to 1300 RPM and using adaptor 2 changes defaut to 1000 RPM. From what you said, If I were to use the 1000 RPM resistor, that should give me sufficient air movement and also be quieter. Do you agree?

Chike said at 12:03 PST
Most time fan is at 680 RPM and vitualy completely silent.

Re: 3 pin fan - 4 pin fan header

That is my CPU fan, my case fan is steady at 1900 RPM but pretty quiet, and exhusted air is about 2c above ambiant.
It really depends on many factors, but it's noice level is low even at 1600 RPM, and 64.3 m³/h isn't that much.